> Based on many years of hands-on training, it's my understanding that when
> doing microbiology, the purpose of flaming the mouth of a bottle, flask, or
> tube is not to sterilize it, but rather to create a brief upward draft of
> air which prevents airborne dust and other contaminants from settling into
> the vessel.
I've heard this explanation before, and frankly I don't believe it: If
anything, creating a draft would tend to cause dust to swirl up all over
the place. Furthermore, the object is flamed, then removed from the flame
for processing. You flame a pipet and a flask, remove them from the
flame, then stick the pipet into the flask or whatever, well away from
It normally isn't necessary to sterilize these objects as in
> most cases they should already be sterile;
It is mostly to take care of little accidents: the finger touching the
pipet, the outside of the cap touching the lip of the flask, etc.
I hardly ever flame anything, and I don't get contaminations. I'm very
good ... :-)
> When you flame the mouth of a vessel, do you
> really wait for it to reach 400C? FWIW, I also use a lot of plastics these
> days and most plastics can't take the heat.
A correctly flamed pipet is hot; second-degree burn hot, sometimes! I know
from painful experience. And I also have lots of half-melted plastic
All told, however, I agree that with today's disposable plastics, flaming
is mostly a thing of the past in laboratories.
Pierre Jelenc I like to have everything so good, I can
Calvin & Hobbes